This invention relates to die sets and dies of the type used in punch presses, and particularly to a rotatable master die set accomodating a quick-change unit die system wherein unit dies may be quickly and easily removed, installed, aligned, and clamped in the master die set. The invention also relates to a method of using such a rotatable master die set to form saw teeth of variable gullet depth using a common unit die.
Die sets for use with a punch press typically have a pair of opposed shoes which are moveable with respect to each other for moving a punch with respect to a die opening. These die sets are commonly installed in a punch press by rigidly fixing one shoe to the bed of the punch press and the other shoe to the ram of the punch press. Prior to installation of the die set in a punch press, a die, consisting essentially of a punch and a mating die opening, are respectively fixed to the opposing shoes of the die set in registry with one another.
The most common method of attaching a die to a die set is with an arrangement of screws and dowels. Such screws typically extend through a smooth bore in the shoe and into a threaded bore in the hardened steel of the die block, making it impossible to remove the screws while the die set is installed in the punch press. The dowels are used to accurately position the die block on the shoe and, accordingly, fit tightly into the holes which are formed into the die block and the shoe. Due to this necessarily tight fit, the die block cannot be lifted off its shoe while the shoe is installed in the punch press, but the shoe must be removed from the press and the dowels drifted out with a hammer and drift. A punch or punch holder would be attached to the opposing shoe of the die set in a similar manner, and would also be difficult and time consuming to remove. Since die sets with installed dies can be quite heavy, they are usually installed and removed from a punch press with the aid of a fork lift or hoist.
Due to the aforementioned difficulties in removing and reinstalling dies on die sets, a die is customarily allowed to remain on a die set and the die sets are changed on the punch press, rather than changing the dies on the die sets. This practice is expensive, necessitating the purchase of many die sets, and is also inconvenient because of the time and equipment required to replace the whole die set on the punch press.
One approach to facilitating the changing of dies is to use master die sets with T-slots or channels formed therein in which replacement dies can be clamped. However, with such a system it is still necessary to perform the time-consuming steps of aligning the punch and die opening in the die set in precise mating relationship with each other each time the die is placed in the die set.
Another approach to this problem utilizes an integral punch and die opening which are mounted in a C-frame so that the punch and die opening are always aligned in registry with one another.
Still another approach has been to use a universal master compound die with interchangeable die parts to enable a single die to make a variety of parts and thereby reduce the number of times it is necessary to change the die. Such a system is provided by the Hovis Screw Lock Company of Warren, Mich.
Another difficulty associated with typical die set-ups is the inconvenience of angularly reorienting the die with respect to the workpiece. As can be easily envisioned, it would be very time consuming to rotate and fix one of the die pieces, then align the independently supported mating die piece and fix it into position. One situation where such a reorientation of the die is desired is in the manufacture of saw blades. A particular saw mill may desire a saw blade having teeth with a deeper or shallower gullet than is standard. The same die may be rotated to form saw teeth of the same tooth size, but of different gullet depth. Rotating and aligning the die pieces separately is very time-consuming, and because it takes up valuable production time, very expensive.